This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-070211, filed Mar. 14, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device using a film type thin insulating substrate as an interposer, and in particular, to a semiconductor device which is adapted to be employed in a thin semiconductor package or in antenna circuit board of an RFID (Radio Frequency Identification) device.
A semiconductor device using a film type interposer according to the prior art includes generally a semiconductor element (hereinafter referred to as a chip) having a plurality of pads, protruded bumps bonded to the pads respectively, and an interposer composed of an insulating film substrate having wiring layers formed of a patterned metal foil, the wiring layers being electrically connected to the bumps.
There are known several kinds of film type interposers which are adapted to be employed in a semiconductor device. Generally, these film type interposers are called an FPC (Flexible Printed Circuit board) and provided in such a manner that a metal foil such as a copper or aluminum foil is adhered onto an insulating polyimide film or an insulating PET film and that the metal foil is etched to provide conductive circuits composed of a large number of conductive layers.
As for the method of bonding a chip to this film substrate, there is known a bonding method wherein a metallic bump is formed on each pad of the chip and then, the chip is bonded to the film substrate by using an ACF (anisotropic conductive film).
FIG. 16A shows a perspective view of a chip according to the prior art, and FIG. 16B shows a cross-sectional view taken along the line 16B-16B of FIG. 16A. Referring to FIGS. 16A and 16B, on a peripheral region of main surface of a chip 101 made of a silicon semiconductor, there are provided a plurality of pads 102 of aluminum, on each of which a plated bump 103 by gold plating is provided. As for the method of forming this bump 103, there is known a method wherein a conductive film called a barrier metal is formed on the main surface of the chip 101, a plating mask is formed using a photoresist, and bumps are selectively formed on the barrier metal by means of electroplating, unwanted portions of barrier metal layer being subsequently removed.
FIG. 17A shows a perspective view of another example of a chip according to the prior art, and FIG. 17B shows a cross-sectional view taken along the line 17B-17B of FIG. 17A. Referring to FIGS. 17A and 17B, on a peripheral region of a surface of a chip 101 made of a silicon semiconductor, there are formed a plurality of pads 102 of aluminum, on each of which a stud bump 104 is provided. The stud bump 104 is formed through the stud bonding of an Au wire, the top surface of the resultant stud being subsequently pressed. More specifically, the stud bump 104 is formed by a method wherein an electrode called a torch rod is placed near a tip of Au wire, and a high voltage is applied between the torch rod and the tip of Au wire to generate a spark discharge therebetween, thereby heating the tip of the Au wire so as to provide a ball which is then pressed to the pad 102 of the chip, using a bonding tool having a capillary, the remainder of the Au wire being then pulled up, and the top surface of the bump thus formed being subsequently pressed to provide the bump.
FIG. 18A shows a perspective view of a film substrate wherein an ACF is adhered onto an insulating film substrate having aluminum wiring layers, and FIG. 18B shows a cross-sectional view taken along the line 18Bxe2x80x9418B of FIG. 18A. Referring to FIGS. 18A and 18B, on the surface of an insulating film substrate 105 of a polyimide film, there is formed an adhesive layer 108, on which aluminum wiring layers 106 are provided. Further, an ACF 107 is provided over the adhesive layer 108 to cover an end of each of the leads for providing the aluminum wiring layers 106.
FIG. 19A shows a perspective view of a device wherein a chip having bumps, which are attached to the chip by the method illustrated in FIGS. 16A and 16B, or in FIGS. 17A and 17B, is placed via an ACF onto an insulating film substrate, and then bonded to the insulating film substrate, thereby electrically connecting the bumps to the wiring layers of the insulating film substrate. FIG. 19B shows a cross-sectional view taken along the line 19Bxe2x80x9419B of FIG. 19A. FIG. 20 is an enlarged cross-sectional view of FIG. 19B, illustrating the bonded portion between the chip and the insulating film substrate. Referring to FIGS. 19A, 19B and 20, in the same manner as the case of bonding of a flip chip, the chip 101 having the bumps 104 is aligned with the wiring layers 106 of the insulating film substrate 105, and bonded thereto under a heated condition so as to cure the resin of the ACF 107, thereby executing not only the bonding of the chip 101 but also the electrical connection between the bumps (stud bumps) 104 and the aluminum wiring layers 106. By the way, the electrical connection between the stud bumps 104 and the aluminum wiring layers 106 is carried out through metallic particles 109 dispersed in the ACF 107.
As described above, the electrical connection between the bumps formed on the pads of chip and the insulating film substrate is realized through the metallic particles 109 added to the ACF 107. For example, in the case of FC262B (ACF, a product from Hitachi Kasei Co., Ltd.), a resin containing a main component of the FC262B is cured at a temperature of 180xc2x0 C. for about 30 seconds. Further, since a suitable amount of Ni particles having a particle size of about 5 to 20 xcexcm is contained in the FC262B as the metallic particles, the electrical connection between the aluminum wiring layers of the insulating film substrate and the bumps of the chip can be provided. Additionally, since the chip and the insulating film substrate are bonded to each other by heating and pressing, the Ni particles are enabled to thrust into the aluminum wiring layers of the insulating film substrate, thereby breaking the oxide film formed on the surface of aluminum wiring layers and making it possible to provide the electric conduction between the bumps and the aluminum wiring layers. However, it has been found through a reliability test such as a temperature cycling test that an oxide film tends to be newly formed on a surface of an easily oxidizable aluminum layer, thereby giving rise to conduction failure. Further, there is also known a paste type anisotropic conductive resin other than the aforementioned film type anisotropic conductive resin. However, since this paste type anisotropic conductive resin also contains metallic particles, problems such as the sedimentation of metallic particles would be caused to occur, thus deteriorating the yield in the electrical connection between the bumps and the aluminum wiring layers.
Next, other problems accompanied with the conventional interposer will be explained with reference to FIGS. 21 to 23.
FIG. 21 illustrates a perspective view of a conventional insulating film substrate having aluminum wiring layers on both surfaces, to which a chip is connected in the same manner as the bonding of the flip chip. FIG. 22 illustrates a cross-sectional view of an insulating film substrate having through-holes, wherein aluminum wiring layers provided on both surfaces of the substrate are connected to each other through the plated through-hole. FIG. 23 illustrates a cross-sectional view of an insulating film substrate having wiring layers on both surfaces, wherein the aluminum wiring layers are connected to each other by mechanical caulking. FIG. 21 shows a perspective view an opposite surface of an insulating film substrate 105 having wiring layers on both sides. Namely, aluminum wiring layers of the main surface of the film substrate 105, on which a chip is mounted, are partially connected to those of the opposite side through a caulking member 111. In FIG. 22, a through-hole is formed in the insulating film substrate 105 so that it penetrates through copper wiring layers 112 provided on both surfaces of the insulating film substrate 105, and plating is applied to the inner surface of the through-hole to form a plated layer 113, thereby electrically connecting both-sided copper wiring layers 112 to one another. In this case, since a plating process is required, the manufacturing cost would be greatly increased. Further, aluminum wiring layers can not be used because they are not adapted to plating. In the case of the method shown in FIG. 23, since the mechanical caulking is employed, it becomes possible to use the aluminum wiring layers 106. However, in order to perform the mechanical caulking, an area of at least 2 mm or more is required, thereby limiting the processing. welding (spot welding) may be employed in the same manner as aforementioned caulking. However, since the welding also requires an area of at least 2 mm or more, the same problem as that of the aforementioned caulking will be raised.
The present invention has been accomplished to overcome the aforementioned problems, and therefore, an object of the present invention is to provide a semiconductor device, wherein bumps each provided on an electrode of a chip are contacted to wiring layers of an insulating film substrate serving as an interposer to obtain excellent electrical connection, and wherein bumps each provided on a pad of a chip are made to pierce both-sided wiring layers or three or more wiring layers provided on an insulating film substrate, thereby accomplishing electrical connections among wiring layers.
Another object of the present invention is to provide a method of producing such a semiconductor device as mentioned above.
According to one aspect of the present invention, there is provided a semiconductor device wherein bumps, each provided on an electrode of a chip and having a sharply pointed configuration or cut grooves, are connected to wiring layers of an insulating film substrate used as an interposer while breaking an oxide film or contaminations formed on a surface of each of the wiring layers. Therefore, highly reliable electrical connection can be provided because a new phase of the material appears. Further, electrical connections among wiring layers can be obtained when the bumps pierce both-sided wiring layers, or three or more wiring layers of the film substrate.
According to another aspect of the present invention, there is provided a method of making a semiconductor device which comprises the steps of: forming a plurality of projected bumps on the pads formed on a surface of a semiconductor chip; preparing an interposer composed of an insulating film substrate having wiring layers formed by patterning of a metal foil; and bonding the bumps to the wiring layers in the form of a flip chip, thereby deforming a tip of each of bumps. The bumps may be composed of gold, and the wiring layers may be composed of aluminum. Another wiring layers may be formed on the opposite surface of the insulating film substrate, and the tip of each bump may be pierced through the insulating film substrate so that the bumps are electrically connected to the wiring layers of the opposite surface of the film substrate.
The tip of each of the bumps may be extended into the interior of the leads of the wiring layers. The bumps may be respectively formed of a stud bump or a plated bump. The tip of each of the bumps may be protruded to the opposite surface of the insulating film substrate. The tip of each of the bumps protruded from the opposite surface of the insulating film substrate may be electrically connected to the wiring layers of the insulating film substrate. The bumps may be composed of a material selected from gold, solder, copper and aluminum. The wiring layers formed on the insulating film substrate may be formed of a material selected from aluminum, copper, gold, silver and a conductive paste. The wiring layers to be formed on the surface of the insulating film substrate may be formed of an aluminum layer, while the bumps may be formed of gold. Furthermore, an adhesive or a thermosetting resin such as an under-fill resin may be interposed between the semiconductor chip and the insulating film substrate.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.